Pedicle screws and spinal stabilization systems of the type described at the outset are known for example from DE 10 2013 100 574 A1. They can be used for example in deformity surgery in order to impart to a deformed spine a desired form and fix it thereinto by appropriate implantation and alignment of pedicle screws. For the alignment of individual malpositioned vertebrae, the forces for the corrective maneuver are introduced into the respective vertebra via the pedicle screws.
In pedicle screw systems which permit top-loading of a connecting element into a corresponding connecting element receptacle on the screw head, i.e. in what are known as “tulip” design systems, an introduction of force is not possible if the pedicle screw is configured in the form of a polyaxial screw. Force introduction is only possible if the screw head is immovable relative to the screw shaft or is, at most, pivotable about a single axis, i.e. if the pedicle screw is what is known as a monoaxial screw. With this design, the screw head is moved in a plane which extends perpendicularly to the axis about which it is pivoted so that in this sense the monoaxial screw can also be referred to as a uniplanar screw. With polyaxial screws, on the other hand, which considerably simplify the insertion of the connecting element, such as a rod, by the screw head being able to be given any desired orientation with respect to the screw shaft, such an introduction of force and correction of a vertebra's alignment is not possible or is possible in only a rudimentary form. In particular, the technique of segmental derotation cannot be applied with polyaxial screws. This technique can only be implemented with the direct introduction of force into the pedicle screw as allowed by the described monoaxial screws in particular.